A question about Limewire?

I have a friend who uses limewire. She told me if limewire was illegal or not. How do they catch you with limewire? I hear if you get caught, you have to pay a HUGH fine. How do you not get caught? Is there a program that can stop people from finding out that you have limewire. If there isn't, does anyone know any places where my friend can get free music but that's not illegal? Also how do people even know how you have limewire in the first place?